In-situ mask technique for producing III-V semiconductor components

ABSTRACT

Method of producing a structure for III-V semiconductor components in which a mask is applied to a sample in a masking step, characterized in that at least one mask material is a monocrystalline III-V semiconductor material. This makes possible an easy in-situ removal of the mask from the semiconductor material, which in turn makes possible the growing of additional layers.

[0001] In the production of III-V semiconductor components, masking steps are usually used to structure the surface of a sample. The surface of the sample is partially covered with a mask, for instance a mask made of SiO₂ as an amorphous material. The sample material is then removed in the region which is not covered by the mask by an etching step (a dry or wet chemical process).

[0002] The term “sample” refers to any material which is structured in the course of manufacturing semiconductor components.

[0003] The disadvantage of this procedure is that, in order to remove the SiO₂ mask from the surface, the sample must be removed from the epitaxy apparatus, thereby exposing the sample to airborne contaminants and oxygen. The contamination is particularly bad in structures containing aluminum, because this comprises a high bonding affinity to oxygen. Since such structures are highly significant to semiconductor laser production, the contamination is particularly problematic.

[0004] It is the object of the present invention to lay out a method by which it is possible to easily remove the mask from semiconductor material and apply additional layers in-situ in the manufacture of III-V semiconductor components. This object is inventively achieved by a method with the features of claim 1.

[0005] Using a monocrystalline III-V semiconductor material in at least one mask material, it is possible to create a “self-dissolving” mask which is removable from the sample in-situ. The mask is dissolved during etching, which saves a substantial amount of processing time.

[0006] It is advantageous if at least one mask material is Ga_(x)In_(1−y)As_(y)P_(1−y) or AlGaInAs. These materials can be removed in a highly controlled fashion by etching the sample.

[0007] It is particularly advantageous when the creation of a structure on and/or in the mask, specifically by lithography, is followed by an etching step with tertiary butyl chloride (TBCl) as the etching agent. This etching agent is appreciably milder than the halogenic hydrogen compounds (e.g. HCl) commonly used in in-situ methods. Moreover, the etch rate of this agent is particularly easy to control.

[0008] It is advantageous to select the etch rate in the etching step in dependence upon the composition of the mask material, so that the mask is dissolved during etching. A self-dissolving mask can thus be created, in which the etch rate is advantageously precisely selected such that the mask is gone from the sample at the end of the etching step.

[0009] The etching step is expediently performed in-situ in the same device in which the structure has been applied in and/or on the sample.

[0010] Advantageously, after the etching step at least one epitaxial layer, particularly a guard layer, is applied to the surface. This is also performed in-situ.

[0011] The semiconductor component that emerges upon completion of the method can expediently be utilized in a semiconductor laser.

[0012] An exemplifying embodiment of the invention will now be described in detail with reference to the Figure of the drawings. Shown are:

[0013]FIG. 1 a flowchart of an embodiment of the inventive method;

[0014]FIG. 2 a graphic representation of measurement values related to the dependency of the etch rate on the composition of the mask material.

[0015] The production of semiconductor components by epitaxy and masking being essentially known, FIG. 1 represents only the steps that are essential to laying out the invention. A wafer serves as substrate. The substrate with the layer structure of the semiconductor component is referred to as a sample. The mask is disposed over the layer system.

[0016] In the first step 1, a component base structure is applied on a wafer by epitaxy. The mask material is also epitaxially applied. This is Ga_(x)In_(1−y)As_(y)P_(1−y) in this case. Alternatively, AlGaInAs can be utilized.

[0017] In the second step 2, the surface of the sample and the mask are structured ex-situ by a known technique such as lithography.

[0018] In the third step 3, the etching step, a structure on and/or in the sample is etched in the epitaxy apparatus. Tertiary butyl chloride (2-Cl-2-methylpropane; TBCl) is used as the etching gas. TBCl is less aggressive chemically than the customary etching gasses such as hydrochloric acid.

[0019] Surprisingly, the etch rate of TBCl in the mask material Ga_(x)In_(1−y)As_(y)P_(1−y) is dependent on the composition of the mask material, i.e. on x and y. This will be described more closely in connection with FIG. 2.

[0020] In the present case, the composition of the mask material is selected such that by the end of the etching step 3 the mask material is gone from the sample. Alternatively, the mask material can be removed up to a predeterminable amount.

[0021] Because this etching is performed in-situ in the epitaxy a apparatus, contamination of the surface is avoided, and valuable processing time is saved.

[0022] Next, in a fourth step 4 additional layers are grown over, particularly epitaxial guard layers. This is particularly advantageous given sample materials containing aluminum, because these are particularly sensitive to contamination.

[0023] Upon completion of the inventive method, the created semiconductor structure can be utilized in a semiconductor laser.

[0024]FIG. 2 represents measurement values in which the dependency of the etch rate (in nm/hr) is plotted on the ordinate. The gallium portion x in the mask material Ga_(x)In_(1−y)As_(y)P_(1−y) (in %) is plotted on the abscissa. The measurement values were obtained at a temperature of 580° C. given a TBCl flow of 8.2×10⁻⁵ mol/min (without PH₃). The hydrogen carrier gas flow amounted to 16 l/min.

[0025] It can be recognized in FIG. 2 that a high etch rate is achieved given a low gallium portion. Given a gallium portion of 10%, the etch rate falls to approximately half. An increase to 15% halves this value again. Thus, the etch rate is approximately linearly related to the gallium proportion.

[0026] With the aid of a functional dependency such as this, the etch rate can be set such that a mask of predetermined thickness is completely gone from the sample at the conclusion of the etching process. If the etch rate is prescribed, the thickness of the mask material can be specified, accordingly, in order to achieve the same aim.

[0027] The invention is not limited in its embodiment to the foregoing preferred exemplifying embodiments. Rather, any number of variations are also imaginable which employ the inventive method and the inventive device in fundamentally different embodiments. 

1. Method of producing a structure for III-V semiconductor components in which a mask is applied to a sample in a masking step, characterized in that at least one mask material is a monocrystalline III-V semiconductor material.
 2. Method as claimed in claim 1, characterized in that at least one mask material is Ga_(x)In_(1−y)As_(y)P_(1−y) or AlGaInAs.
 3. Method as claimed in claim 1 or 2, characterized in that following the creation of a structure on and/or in the mask (2), particularly by lithography, an etching step (3) is performed in which tertiary butyl chloride is utilized as the etching agent.
 4. Method as claimed in at least one of the preceding claims, characterized in that the etch rate in the etching step (3) is selected in dependence upon the composition of the mask material, so that the mask is dissolved during the etching.
 5. Method as claimed in claim 4, characterized in that the etch rate is precisely selected such that the mask is gone from the sample at the end of the etching step (3).
 6. Method as claimed in claim 4 or 5, characterized in that the etching step (3) is performed in-situ in the same apparatus in which the structure was previously applied in and/or on the sample.
 6. Method as claimed at least one of the preceding claims, characterized in that following the etching step (3), at least one epitaxial layer, in particular a guard layer, is applied to the surface.
 7. Method as claimed in at least one of the preceding claims, characterized in that upon completion of the method the sample can be used in a semiconductor component, in particular a semiconductor laser. 